The Oxymax W COS41 is a potentiostatic amperometric two-electrode oxygen sensor for measuring dissolved oxygen in water and wastewater applications. It features a long-term stable, membrane-covered sensor that requires minimal maintenance and calibration. The sensor measures oxygen concentration and outputs the results in mg/L, % saturation, or hPa. It can be used for applications like sewage treatment, water monitoring, water treatment, and fish farming.

1. TI284C/07/en/02.07
51506689
Technical Information
Oxymax W COS41
Potentiostatic amperometric two-electrode sensor
Long-term stable sensor for water and wastewater applications
Application
The continuous measurement of the dissolved oxygen
concentration is very important in many areas of water
management:
• Sewage treatment plants:
Oxygen measurement and regulation in the activated sludge
basin for a highly efficient biological cleaning process
• Water monitoring:
Oxygen measurement in rivers, lakes or seas as an indicator of
the water quality
• Water treatment:
Oxygen measurement for status monitoring of drinking water
for example (oxygen enrichment, corrosion protection etc.)
• Fish farming:
Oxygen measurement and regulation for optimum living and
growth conditions
Your benefits
• Maximum measurement accuracy:
– Long maintenance intervals
– Intelligent sensor self monitoring
• Membrane covered sensor, i.e.:
– high O2 selectivity
– Minimum maintenance effort
– Minimum calibration effort thanks to simple calibration in
air

2. Oxymax W COS41
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Function and system design
Measuring principle The oxygen molecules diffused through the membrane are reduced to hydroxide ions (OH-) at the cathode.
Silver is oxidized to silver ions (Ag+) at the anode (this forms a silver halogenide layer).
A current flows due to the electron donation at the cathode and the electron acceptance at the anode. Under
constant conditions, this flow is proportional to the oxygen content of the medium.
This current is converted in the transmitter and indicated on the display as an oxygen concentration in mg/l,
as a saturation index in % SAT or as an oxygen partial pressure in hPa.
Measuring system A complete measuring system comprises at least:
• Oxygen sensor
• Transmitter, e.g. Liquisys M COM223/253
• Special measuring cable
• Assembly, e.g. flow assembly COA250, immmersion assembly CYA611 or retractable assembly COA451
Optional:
• Universal suspension assembly support CYH101 for immersion operation
• Junction box VBM (with cable extension)
• Automatic spray cleaning system Chemoclean
a0004101
Measuring system (example)
1 Junction box VBM (optional)
2 Transmitter Liquisys M COM253
3 Special measuring cable
4 Immersion assembly
5 Oxygen sensor
Input
Measured variable dissolved oxygen [mg/l, ppm, % SAT or hPa]
Measuring range with Liquisys M COM 223/253-DX/DS:
0.05 ... 20.00 mg/l (ppm)
0.00 ... 200 % SAT
0 ... 400 hPa

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Wiring
Electrical connection Direct connection to the transmitter
The sensor is connected using a special measuring cable. The wiring diagram is contained in the Operating
Instructions of the COM223/253-DX/DS transmitter.
Connection with cable extension
To lengthen the sensor connection beyond the length of the fixed cable, you require a junction box VBM. The
connection is lengthened to the transmitter using the special measuring cable CYK71.
a0004127
Connection via junction box VBM
1 Sensor
2 Junction box
3 Extension cable
4 Transmitter
a0004119
Special measuring cable CYK71
Terminal
S
12
90
91
11
Assignment
Outer shield
Active inner shield (NTC)
Cathode
Anode
NTC temperature sensor
BN
GN
WH
RD
S
12
90
91
11
a0004126-en
Junction box VBM, side view
a0004125-en
Junction box VBM, top view
54/2.13
mm/inch
Pg 13,5
52/2.05
80/3.15
113/4.45
125/4.92
62.5/2.46
10/0.09
136/5.35
mm/inch

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Performance characteristics
Response time T90: 3 minutes
T99: 9 minutes (each at 20 °C (68 °F))
Reference operating
conditions
Signal current in air1) approx. 300 nA
Zero current zero current free
Measured value resolution 0.01 mg/l (0.01 ppm)
Maximum measured error ±1 % of measured value2)
Long-term drift with permanent polarization: < 1 % per month
Influence of medium pressure Pressure compensation not necessary
Polarization time < 60 minutes
Oxygen intrinsic consumption Approx. 90 ng/h in air at 25 °C (77 °F)
Installation
Angle of installation The sensor can be installed up to the horizontal in an assembly, support or a suitable process connection. Other
angles are not permissible. Do not install the sensor overhead.
a0004088
Angle of installation
A Permissible installation positions: 0 ... 180 °, overhead installation is not permitted
! Note!
Make sure you comply with the instructions for installing sensors. You will find them in the Operating
Instructions for the assembly used.
Reference temperature: 25 °C (77 °F)
Reference pressure: 1013 hPa (15 psi)
1) For the reference operating conditions indicated
2) In accordance with IEC 746-1 at nominal operating conditions

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Environment
Ambient temperature range –5 to 50 °C (20 to 120 °F)
Storage temperature filled with electrolyte: –5 to 50 °C (20 to 120 °F)
without electrolyte: –20 to 60 °C (0 to 140 °F)
Ingress protection • Fixed cable versions:
IP 68 (10 m (33 ft) water column at 25 °C (77 °F) in 30 days)
• Top 68 plug-in head versions:
IP 68 (1 m (3.3 ft) water column at 50 °C (122 °F) in 7 days)
Process
Process temperature –5 to 50 °C (20 to 120 °F)
Process pressure max. 10 bar (145 psi) permissible overpressure
Underpressure operation is not permissible.
Mechanical construction
Design, dimensions
Weight with cable length 7 m (23 ft): 0.7 kg (1.5 lbs.)
with cable length 15 m (49 ft): 1.1 kg (2.4 lbs.)
with TOP68 plug-in connection: 0.3 kg (0.66 lbs.)
a0004085-en
Fixed cable version
a0004086-en
TOP68 version
171
/
6.73
Ø40 / 1.57
144
/
5.67
190
/
7.48
mm / inch
171
/
6.73
144
/
5.67
190
/
7.48
mm / inch
Ø40 / 1.57

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Material
Process connection G1 and NPT ¾"
Maximum cable length max. 50 m (164 ft)
Membrane thickness approx. 50 μm
Electrolyte Alkaline electrolyte
Ordering information
Product structure
Scope of delivery The following items are included in the delivery:
• Oxygen sensor with transport protection cap for membrane protection
• Accessories set with the following contents:
– 2 replacement cartridges (replacement membrane caps)
– 10 plastic ampoules containing electrolyte
– 1 sealing kit with 3 O-rings
– 6 abrasive sheets
• Operating Instructions (on CD only)
• Brief Operating Instructions (paper version)
Sensor shaft:
Membrane cap:
Cathode:
Anode/Reference electrode:
POM
POM
Gold
Silver / silver bromide
Cable length
2 Cable length: 7 m (22.97 ft)
4 Cable length: 15 m (49.22 ft)
8 Without Cable (TOP 68 version only)
9 Special design to customer specifications
Cable connection
F Fixed cable connection
S Cable connection using TOP 68 plug
COS 41- Complete order code

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Accessories
! Note!
In the following sections, you find the accessories available at the time of issue of this documentation.
For information on accessories that are not listed here, please contact your responsible service.
Assemblies (selection) Flow assembly COA250
• for sensor installation in pipe lines, PVC
• ordering acc. to product structure (Technical Information TI111C/07/en)
Immersion assembly Dipfit W CYA611
• for sensor immersion in basins, open channels and tanks, PVC
• ordering acc. to product structure (Technical Information TI166C/07/en)
Zero solution • 3 units to produce 3 x 1 liter oxygen-free solution
• order no. 50001041
Measuring cable COK41 special measuring cable
• for COS41 oxygen sensors with TOP68 plug-in head
• Order numbers:
– Cable length 7 m (23 ft): 51506817
– Cable length 15 m (49 ft): 51506818
CYK71 measuring cable
• non-terminated cable for the connection of sensors (e.g. conductivity sensors) or the extension of sensor
cables
• Sold by the meter, order numbers:
– non-Ex version, black: 50085333
– Ex version, blue: 51506616
Junction box Junction box VBM
• For cable extension, with 10 terminals
• IP 65 (i NEMA 4X)
• Material: aluminum
• Order numbers:
– cable entry Pg 13.5: 50003987
– cable entry NPT ½": 51500177
Transmitter Liquisys M COM 223/253
• Transmitter for oxygen measurement
• field or panel-mounted housing
• Hart® or Profibus available
• Ordering acc. to product structure, see Technical Information (TI 199C/07/en)

8. Instruments International
Endress+Hauser
Instruments International AG
Kaegenstrasse 2
4153 Reinach
Switzerland
Tel.+41 61 715 81 00
Fax+41 61 715 25 00
www.endress.com
info@ii.endress.com
TI284C/07/en/02.07
51506689
Printed in Germany / FM+SGML 6.0 / DT